Time-of-use and demand metering in conditions of power outage

ABSTRACT

A metering system for metering the consumption of electrical energy to provide time-of-use and demand metering in the presence of at least one power outage event includes an encoder device for transmitting a radio frequency (RF) signal and a interrogate/receiver device for receiving the radio frequency signal transmitted by the encoder device. The encoder device has apparatus for sensing electrical power consumption and for sensing a power outage. Additionally, the encoder device has apparatus for periodically generating an encoded RF signal for transmission by the encoder device. The signal has a plurality of discrete components, each of the components being related to electrical power consumption over a selected interval of time. The signal further has a power outage flag associated with each discrete component, the flag being set for any interval of time during which a power outage is sensed. A meter counter for incrementally increasing a count as a function of time is included. The meter counter is powered by the electrical power being metered. The interrogate/receiver device has a decoder that is communicatively coupled to the encoder device for decoding the encoded RF signal received from the encoder device. A receiver counter for incrementally increasing a count as a function of time is asynchronous with respect to the meter counter.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional application Ser.No. 60/059,170, filed Sep. 17, 1997, which is incorporated herein in itsentirety by reference.

TECHNICAL FIELD

The present invention relates to the metering of the consumption ofelectrical energy. More particularly, the present invention relates toproviding advanced metering functions when power is temporarily lost atthe meter.

BACKGROUND OF THE INVENTION

The advanced metering functions that must be accommodated by a radiofrequency (RF) transmitting meter include both demand and time-of-usemetering. A review the basics of both demand and time-of-use metering isprovided by way of background.

With respect to demand metering, the following paragraph comes from theHandbook for Electricity Metering, Edison Electric Institute:

"Kilowatt demand is generally defined as the kilowatt load averaged overa specified interval of time. The meaning of demand can be understoodfrom FIG. 1, which shows an example power curve over time. In any one ofthe time intervals shown, the area under the dotted line `demand` isexactly equal to the area under the power curve. Since energy is theproduct of time and power, either of these two areas represents theenergy consumed in the demand interval.

The equivalence of the two areas shows that the demand for the intervalis that value of power which, if held constant over the interval, willaccount for the same consumption of energy as the real power. Demand canthen be defined as the average of the real power over the interval."

Referring to FIG. 1, the horizontal axis is time and the vertical axisis units of power in kilowatts (kW). Typical electric meters recordconsumption in units of kilowatt-hours (kWh), which is an energy value.For instance, in a first case an electrical meter would register one kWhconsumption if one kW were used constantly for one hour. Similarly, in asecond case the meter would show one kWh consumption at the end of anhour if two kW were used constantly for the first half hour with noenergy used in a second half hour. Finally, in a third case the meterwould also show one kWh consumption at the end of an hour if twelve kWwere used constantly for the initial five minutes of the one hourinterval and no energy was used in the remaining 55 minutes. FIG. 1illustrates the foregoing over four demand intervals having a varyingpower curve. Demand is the area under the dotted line in each of thedemand intervals. The area under the dotted line equals the area underthe power curve equals total energy for the interval. Demand then foreach of the four demand intervals equals the average power over theindividual demand intervals.

The aforementioned three cases are depicted in Table 1. The bottom entryin Table 1, labeled "Electric Meter Value Registered at End of TimePeriod", shows the increase in consumption which would be recorded onthe electric meter at the end of each hour for each of the three casespresented. All of the three cases are shown to have the sameconsumption. From a pure consumption point of view all cases would thenhave the same electric bill for the one hour demand interval.

                  TABLE 1    ______________________________________    Scenarios Showing Consumption Recorded by an Electric    Meter for Different Power Levels and Times of Usage                 Case 1  Case 2    Case 3    ______________________________________    Constant Power Level                   1 kW      2 kW      12 kW    Time at Constant Power                   60 minutes                             30 minutes                                       5 minutes    Usage    Time at Zero Power Usage                   0 minutes 30 minutes                                       55 minutes    Total Time Period Evaluated                   1 hour    1 hour    1 hour    Electric Meter Value Regis-                   1 kWh     1 kWh     1 kWh    tered at End of Time Period    ______________________________________

Demand billing is related to demand as distinct from the aforementionedconsumption billing. The electric utility must be geared to meetingdemand, not just average consumption. There are a number of differenttypes of demand billing. Block demand is a frequently used form ofdemand billing. Referring to FIG. 2, time is displayed on the horizontalaxis and power is displayed on the vertical axis. As displayed on thehorizontal axis there are four intervals, A-D, that comprise a singleblock. Block demand calculates demand over the intervals A-D comprisingthe block. Consumption is recorded over the interval and divided by atime period, in hours, that the interval comprises. Repeating this forall the intervals in a block would allow billing based on the averagedemand over the block. Most often, however, the maximum demand is billedfor the entire period of the block. FIG. 2 illustrates the demand foreach interval as being indicated by the area under the dashed line. Inpractice, the maximum demand, depicted in interval C, is the demand thatwould be billed to the customer over the entire period comprising theblock.

Rolling demand is another frequently used form of demand billing.Rolling demand may be thought of as a sliding window of block demands.As indicated in FIG. 3, for rolling demand the time scale on thehorizontal axis is still divided into individual intervals. However, thetime scale is further divided into sub-intervals, as depicted. Insteadof calculating the demand at the end of each interval, the calculationis performed by adding the consumption for a set number of sub-intervalsand then dividing by the time period, in hours, of the compositeinterval. Rolling demand permits greater accuracy in demand billing.Total demand, average demand, maximum demand, and average maximum demandduring a full interval are all types of demand billing that aresupported by calculating rolling demands. Once the rolling demand isknown, any of the aforementioned types of demand billing may be used.

Table 2 presents the same three cases as previously presented withrespect to Table 1. Assuming that the demand sub-interval for billing isfive minutes, the demand over the total hour billing period would becalculated for each interval with each interval being comprised of threesuccessive five minute periods. Over the whole billing period, alldemand value from these intervals will be compared with the largest onebeing used for billing purposes. As depicted in FIG. 3, the maximumdemand is calculated in the eighth interval from the beginning of theone hour time period.

                  TABLE 2    ______________________________________    Scenarios Showing Consumption and Demand Recorded by an    Electric Meter for Different Power Levels and Times of Usage                 Case 1  Case 2    Case 3    ______________________________________    Constant Power Level                   1 kW      2 kW      12 kW    Time at Constant Power                   60 minutes                             30 minutes                                       5 minutes    Usage    Time at Zero Power Usage                   0 minutes 30 minutes                                       55 minutes    Total Time Period Evaluated                   1 hour    1 hour    1 hour    Consumption Value                   1 kWh     1 kWh     1 kWh    Registered at    End of Time Period    Demand Interval Period                   5 minutes 5 minutes 5 minutes    Max Consumption During                   1 kWh     2 kWh     12 kWh    Interval    Maximum Demand Recorded                   12 kW     24 kW     144 kW    at End of Time Period    ______________________________________

To find the maximum demand calculation for the same three cases thatwere presented with reference to Table 1, assume that the time intervalcommences at the start of the hour. With twelve distinct five minutedemand subintervals throughout the hour, demand for each interval mustbe calculated. The calculations for the cases presented in FIG. 2 aresimple since an assumption of level power consumption is made.

For case 1, each of the twelve minute sub-intervals would have the samedemand value of 12 kW. Accordingly, the maximum demand for this case is12 kW and the billing would be for 12 kWh.

For case 2, six of the intervals have a demand value of 24 kW while theremaining six intervals have a demand of 0 kW. So, for case 2, themaximum demand is 24 kW over the entire period of billing and thebilling would be for 24 kWh.

For case 3, only one of the five minute intervals has a demand value of144 kW. The other eleven have 0 kW demand. Accordingly, the maximumdemand in this case is 144 kW and the customer would be billed 144 kWhfor the hour.

The bold text in Table 2 compares the different billing approaches. Froma straight consumption perspective, all three cases are billed the sameas indicted in Table 1. However, when the demand is billed, it is clearthat a maximum demand billing will distinguish the cases drawing heavyloads for relatively short periods. It shows the advantages to theelectric utility for demand metering. The utilities typically desirethis billing method since the cost of supplying energy to a customerdepends on the needed capacity of the utility. This cost translatesdirectly into demand.

We turn now to defining a time-of-use metering. Time-of-use meteringrecords consumption during selected periods of time taken from a largerperiod of time. Typically the larger period of time is a day or a week.Rather than providing the utility with the capability to only charge theuser for the energy used, rates structured on time-of-use informationcan account for when the energy is used. This allows utilities to chargepremiums for energy drawn during peak periods (typically during thedaytime) and provide lower rates for energy drawn during low usageperiods (typically during nighttime).

Referring to FIG. 4, it is assumed that the utility has set up atwo-rate time-of-use billing option. Rate A, the low rate, applies toenergy drawn during the low usage periods. As depicted in FIG. 4, thisoccurs from 12:00 a.m. to 8:00 a.m. and from 6:00 p.m. to 12:00 a.m.Rate B, the high rate, applies to energy drawn during the high usageperiods which, as depicted in FIG. 4, occur from 8:00 a.m. to 6:00 p.m.Utilization of this method for billing is relatively straightforward.For the depicted example day, from midnight to 8:00 a.m., 5 kWh ofenergy was used. Similarly, 20 kWh of energy was consumed from 8:00 a.m.until 6:00 p.m. Finally, from 6:00 p.m until the next midnight, 5 kWh ofenergy was used. Accordingly, the bill for this day will be based on 10kWh at rate A, 20 kwh at rate B.

Time-of-use and demand metering both require a solid, reliable, andaccurate time reference to support billing. An RF based system typicallyincludes a meter transmitter or encoding device located at the site ofthe meter and a remote receiver or reading device. In an RF basedsystem, the consumption message transmitted from the encoding devicedoes not contain a time reference. A time reference is, however,typically stamped to the consumption message by the reading device as itis read by the reading device. This assures that the consumption sentwas the consumption at the time of transmission and that the read deviceclock is accurate and reliable. It has been shown that an RF system willoccasionally miss reading a transmission of a consumption message.System design allows for only a certain percentage of message readreliability, which is always less than 100%. Because of this, a typicalcompensation approach is to transmit multiple consumption messages at atime. This compensation approach typically transmits the last Nconsumptions recorded at the meter in predefined t.sub.Δ intervals. Thereading device then decodes this message to have an accurate consumptionhistory over the last N predefined t.sub.Δ intervals. Therefore, thereading device only needs to decode one out of every N transmissions inorder to receive an accurate consumption message.

The aforementioned compensation approach is typically designed so thatthe desired reliability is achieved under normal operating conditions.The compensation approach adequately supports the advanced meteringfunctions of time-of-use and demand billing. However, a problem existswhen power is lost at the meter due to a power outage. Since there is noon-board time-of-day clock in the encoding device at the meter, there isno time reference available to be encoded. The encoding device ispowered by the power at the meter that is being metered. Any counter inthe encoding device shuts down when power is lost during a power outage.

This means that the consumption information transmitted by the encodingdevice has no reliable time reference with it. When the reading devicedetects and decodes the N consumption values, it can only accuratelytime stamp the most recent value. All the previous N-1 values cannot bereliably time stamped because, if a power outage has occurred, it is notknown when the power outage occurred or the duration of the poweroutage. This greatly degrades the ability of such a system to supportboth time-of-use and demand billing in the presence of a power outage.Accordingly, there is a need in the industry for an RF based encodingdevice and associated receiving device that have the ability to supportboth time-of-use and demand billing, even in the presence of poweroutages observed at the meter.

SUMMARY OF THE INVENTION

The present invention has the capability of maintaining the timereference needed to support both demand and time-of-use billing by anelectric utility with an RF based system. Since there are many millionsof electrical meters currently in existence, any device that must beadded to such a meter must have very low cost. Accordingly, the presentinvention is capable of supporting the advanced metering demanded byutilities with inexpensive component building blocks. Such buildingblocks include a microprocessor, an EE Prom, and simple power supplies.The present invention has the ability to accurately time stamp, withoutambiguity, all consumption data in a period in which a single poweroutage is experienced. Further, the present invention has the ability toaccurately time stamp, without ambiguity, some consumption data in aperiod in which multiple power outages occur. The present inventionperforms these functions with no need to synchronize clocks in theencoder device in the read device and without the need to provide backupbattery power at the meter to power a clock in the event of a poweroutage. The present invention has the ability to maintain powerconsumption history, as well as current consumption, through periods inwhich a power outage occurs.

A metering system for metering the consumption of electrical energy toprovide time-of-use and demand metering in the presence of at least onepower outage event includes an encoder device for transmitting a radiofrequency (RF) signal and a receiver device for receiving the radiofrequency signal transmitted by the encoder device. The encoder devicehas apparatus for sensing electrical power consumption and for sensing apower outage. Additionally, the encoder device has apparatus forperiodically generating an encoded RF signal for transmission by theencoder device. The signal has a plurality of discrete components, eachof the components being related to electrical power consumption over aselected interval of time. The signal further has a power outage flagassociated with each discrete component, the flag being set for anyinterval of time during which a power outage is sensed. A meter counterfor incrementally increasing a count as a function of time is included.The meter counter is powered by the electrical power being metered. Thereceiver device has a decoder that is communicatively coupled to theencoder device for decoding the encoded RF signal received from theencoder device. A receiver counter for incrementally increasing a countas a function of time is asynchronous with respect to the meter counter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphic representation of power consumption with powerrepresented on the ordinate and time represented on the abscissa;

FIG. 2 is a graphic representation of power consumption with powerrepresented on the ordinate and time represented on the abscissadepicting maximum demand billing over a block of time;

FIG. 3 is a graphic representation of power consumption with power onthe ordinate and time on the abscissa depicting a rolling demand typebilling calculation;

FIG. 4 is a graphic representation of power consumption with power onthe ordinate and time on the abscissa depicting a time-of-use billingover a one day billing cycle;

FIG. 5 is a schematic representation of the automatic/remote RFinstrument monitoring system of the present invention;

FIG. 6 is a graphic representation of the effect of a power outage on aninterval in which power consumption data is recorded;

FIG. 7 is a representation of a buffer assigned in the nonvolatilememory of the encoder microprocessor;

FIG. 8 depicts a pointer in the encoder microprocessor that indicatesthe encoded consumption value which occurred at the most recentinterval;

FIG. 9 depicts the pointer of FIG. 8 incremented by one bin;

FIG. 10 is a graphic representation having count value on the ordinateand time on the abscissa depicting the different slopes of the encodercounter and the interrogate/receiver counter;

FIG. 11 depicts the impact of a power outage on the counters depicted inFIG. 10;

FIG. 12 is a graph of count value on the ordinate and time on theabscissa depicting a single power outage occurring in the ninthsub-interval of a consumption interval; and

FIG. 13 is a graph of count value on the ordinate and time on theabscissa depicting two power outages in a single interval.

DETAILED DESCRIPTION OF THE DRAWINGS

A communication system that is more particularly an automatic/remote RFinstrument monitoring system is illustrated generally at 10 in FIG. 5.As shown, automatic/remote instrument monitoring system 10 is adaptedfor use with a plurality of remotely located parameter sensinginstruments such as meters 12A-12C. Meters 12A-12C sense or monitor aphysical parameter, such as a quantity of a given commodity (e.g.electrical power) used by a residential or business customer. The meters12A-12C sense are also capable of sensing a power outage in the casewhere the meters 12A-12C sense are sensing electric power consumption.

Associated with and operatively coupled to each meter 12A-12C is aencoder 14A-14C. Each encoder 14A-14C is a transponder and includes anantenna 16A-16C, respectively, for receiving and transmitting radiofrequency (RF) signals as well as a microprocessor, including a randomaccess memory (RAM), an EEProm, and rather simple power supplies. Itshould be noted that the power supplies do not require battery-suppliedbackup power in the present invention. Encoders 14A-14C accumulate anddigitally store parameter data (including power outage) sensed by meters12A-12C, respectively. Parameter data, as well as other accountinformation such as identification data identifying meters 12A-12C fromwhich the parameter data was sensed, is encoded for transmission in anRF encoder signal by encoders 14A-14C when the encoders 14A-14Cactivated, or polled.

Instrument monitoring system 10 also includes an interrogate/receiverdevice 18. Interrogate/receiver device 18 includes transmitter activator20, receiver 22, which includes a decoder 23, controller 24, and dataprocessor 26 which are preferably carried by a mobile vehicle 28 such asa van. In such other embodiments (not shown), interrogate/receiverdevice 18 is stationary at a selected site with the reception area ofthe various encoders 14A-14C to which the interrogate/receiver device 18is linked. Transmitter activator 20 transmits RF activation signals toencoders 14A-14C via antenna 30, while RF encoder signals from encoders14A-14C are received by receiver 22 through antenna 32. Alternatively,the encoders 14A-14C may be programmed to "bubble-up" a message on aninternal schedule without external activation. Preferably, such amessage is "bubbled-up" every four to five seconds.

Transmitter activator 20 of interrogate/receiver device 18 will generatea polling or activation signal which is transmitted through antenna 30.In the embodiment shown, vehicle 28 will proceed down a roadway,carrying interrogate/receiver device 18. All encoders 14A-14C withinrange of transmitter activator 30 will be activated, or "wake-up" uponreceipt of the activation signal through their antennas 16A-16C.Alternatively, the interrogate/receiver device 18 may be disposed at afixed site within the reception range of the encoders 14A-14C andreceive the "bubbled-up" messages from the encoders 14A-14C.

Once activated, encoders 14A-14C produce and transmit their RF encodersignals which includes the parameter and identification data for Ndifferent t.sub.Δ intervals. The t.sub.Δ intervals are typicallyselected to be rather short, for example, 1.5, 2.5 or 5.0 minutes. Thenumber of different intervals covered in a single transmission is afunction of the design of the automatic/remote instrument monitoringsystem 10. In a preferred embodiment, N equals 48. Encoder signals arereceived by receiver 22, and the data contained therein is decoded. Thisdata is then further processed, and stored, by data processor 26 underthe control of controller 24. On a defined interval, preferably once aday, or after all meters 12A-12C have been read, all parameter,identification, and other account information is transferred to autility billing system 36 through a storage medium, serial datainterface, or other data transmission scheme. These and other featuresof instrument monitoring system 10 are described in greater detail inthe above-identified co-pending application.

Encoders 14A-14C all function in a similar manner, and are preferablyidentical to facilitate high volume, low cost construction. To this end,encoders 14A-14C can utilize a custom large scale integrated circuit,and only a few other components. All subsequent descriptions aretherefore made with referenced to encoder 14A, which is representativeof encoders 14A-14C.

A number of different compensations are designed into the presentinvention in order to permit the encoder device 14 to transmitinformation to the interrogate/receiver device 18 sufficient to satisfythe utilities' billing requirements for an interval in which at leastone power outage occurs. The first such compensation deserves mention asit is a key to solving the overall problem. This compensation is toprovide a power outage flag for each of the N different t.sub.Δintervals. This flag is set if at least one power outage occurs in aninterval. If there are not any power outages in an interval, the flagremains cleared. This first compensation applies to all types of billingused by the utilities, including time-of-use and demand billing.

Demand metering compensations focus on ensuring that all of the N (in apreferred embodiment, N=48) consumption values are stored tonon-volatile memory of the encoder 14 microprocessor between the timethat power is first starting to droop and when power is totally lost.For pure demand billing (not combined with time-of-use), the demandinterval is not defined by a time period on a clock, but rather by atime period for which power is available. Take the example of a demandinterval t.sub.Δ set at five minutes. If power is lost two and one-halfminutes into the interval t.sub.Δ, the interval t.sub.Δ will then endtwo and one-half minutes after power is eventually reapplied and thedemand over the five minute interval and over the period of the poweroutage (in which there is no demand) is accurately sensed. Thissituation is diagrammed in FIG. 6. In interval 1, power is available andthe interval terminates at a time that is equal to the time of theinterval. In interval 2, a power outage occurs during the interval at2a. Power is restored at 2b. The interval 2 is then extended (interval 2equals the time from the interval start at 2 until the successiveinterval commences at 3) in real time by an amount of time equal to theduration of the power outage.

In order to maintain the string of consumption, the N values are writtento non-volatile memory in the encoder device 14 each time that they arerecalculated. This means that following recalculation, there will be anew N value, while the former N value is moved to the N-1 position, theold N-1 value in the N-2 position, the old N-2 value in the N-3position, and so on.

There are two limitations to this approach. First and foremost, thenon-volatile memory is reliable for only for a finite number of writes(in a known non-volatile memory, reliability exists for only one millionwrites). With consumption interval, t.sub.Δ, at a typical value of 11/4minutes, the non-volatile memory would only be reliable for about 21/4years, that is, it would take only 21/4 years to write a million times.An electric meter must have much longer reliability to be acceptable.

The second limitation involves the required write time. It is likelythat the overhead needed to rewrite the string of N values at everyinterval t.sub.Δ would unduly tax the microprocessor of the encoderdevice 14.

The solution to the problem presented by the aforementioned limitationsborrows from the previously described approach of storing the newconsumption data at every interval t.sub.Δ. The key is to recognize thatwhen the historical string of N data points is recalculated, only onevalue in that string changes. All the rest remain the same, but aremoved back one location in the chain.

To accomplish the desired task, a buffer is assigned in the non-volatilememory of the encoder 14 microprocessor. The length of the buffer equals(N-1). Each buffer position is wide enough to store the consumptiondata. In a preferred embodiment, the consumption data is storeddifferentially using nine bits. Given that the non-volatile memory in apreferred embodiment is only byte addressable, there needs to be twobytes allocated to each message. FIG. 7 shows the setup of the buffer.FIG. 7 depicts the bins as 0 through N-2 only for descriptive purposes.In total, this includes N-1 (preferably 47) bins. The Nth (48th) bin isthe most recent full consumption bin, which is 24 bits long andallocated to memory outside of this buffer. The algorithm to store theconsumption data uses this memory as a circular buffer.

A six bit pointer in the encoder 14 microprocessor indicates a positionin the buffer. The pointer indicates the N-1 value, the differentiallyencoded consumption value which occurred at the most recent interval .The adjacent bins hold the N-2 value, the differentially encodedconsumption at the 2nd most recent interval and the N-47 value, thedifferentially encoded consumption value which occurred forty-sevenintervals prior. FIG. 8 depicts these relationships.

When the consumption interval ends, a new consumption value becomes themost recent. A new N-1 differential consumption value is calculated andall the existing historical differential consumption values shift theirtime reference down by one, e.g., N-6 becomes N-7. The existing N-47value falls off of the list, being replaced by the previous N-46 value.

Simply moving the pointer simplifies the shift process. As FIG. 9 shows,incrementing the pointer by one bin points to the old N-47 value.Replacing this value with the new N-1 value shifts the relative timeposition of all the other values by one bin without ever having tophysically move any bits in memory, that is without ever having torewrite any of the values, thereby substantially extending thereliability of the non-volatile memory. The moving pointer keeps thereferences appropriately aligned.

The biggest advantage in using this circular pointer is not insimplifying the shift process. It is in enhancing memory reliability.With the circular pointer it is easy to see that an individual memorylocation will only be written to once every N-1 intervals. Thistranslates directly into the reliability of the device; if N-1 is twiceas large, meaning you write to an individual memory address half asoften, the device's lifetime increases by a factor of 2.

In this method, only the most recent full consumption value, which canbe thought of as the N-0 value, is written to non-volatile memory atpower loss. The 6 bit historical consumption buffer pointer is alsowritten to non-volatile memory at power loss along with theaforementioned full consumption value.

Pure demand is provided with the aforementioned algorithm through poweroutages, as the current differential value is always stored tonon-volatile memory. Additionally, as Table 3 shows, the reliability ofthe non-volatile memory exceeds any reasonable lifetime.

                  TABLE 3    ______________________________________    Estimated Memory Lifetime Using Proposed Approach    Differential    Storage Interval,              t.sub.Δ  Intervals per                                      Years    t.sub.Δ              Year        Writes per Year*                                      per Failure**    ______________________________________      5 Minutes              105120      2237        447     2.5 Minutes              210240      4473        224    1.25 Minutes              420480      8946        112    ______________________________________     *Assuming N - 1 = 47     **Based on a 1 Million Write Reliable nonvolatile memory

In a preferred non-volatile memory, the non-volatile memory addressesonly words and two bytes are allocated for each differential consumptionstorage. Since the differentiation is only nine bits long, this leavesseven bits unused. These bits may be used advantageously as desired toprovide error correcting, checksums, etc. in order to enhance thereliability of the differential consumption message.

As discussed earlier the time dependence needed for time-of-use billingis different than for demand billing. Time-of-use rates transition atprogrammable times of the day. That means that there has to be adequatetime resolution to place the differential consumption values into theproper time-of-use bin. A previous background discussion stated ingeneral terms how to achieve this resolution under normal operation.

When power is lost, the interrogate/receiver device 18 does not knowwhen the outage occurred or for how long it occurred, because there isno internal real time clock or battery backup in the encoder device 14.This becomes critical for time-of-use, as it leads to ambiguity in timestamping the N consumption intervals. Through the addition of the poweroutage flags discussed above, some of the ambiguity can be eliminated byidentifying the interval in which the outage occurred.

This supports the simple means of providing time-of-use metering. Itinvolves time stamping all of the interval data from the most recentconsumption back to the interval where the first power outage occurred.For the intervals prior to the outage, an algorithm is used to classifythe data into billable time-of-use bins.

Table 4 shows an example situation for binning the time-of-use datausing this method. The algorithm chosen for the example states that anyconsumption data which cannot be time stamped gets assigned to the sametime-of-use bin as the bin in which the earliest time stampedconsumption value occurred. For this example, that means the non-timestamped values go into the same time-of-use bin as the N-2 sample. Thepotential for error is shown by comparing the Actual time-of-use Bin andthe Billed time-of-use Bin columns. In the depicted case, a power outageoccurs during the N-3 interval and the time-of-use bin transitions fromthe B rate to the A rate during the N-4 interval. The consumption in theN-4 to N-47 intervals should be billed at the A rate but are in factbilled at the B rate due to the ambiguity introduced by the power outagethat occurs in the N-3 interval.

                  TABLE 4    ______________________________________    Example of TIME-OF-USE Binning Through Power    Outage Using Simple Algorithm            Power   Able to    Actual Billed    Historical            Outage? Time Stamp TIME-  TIME-    Consumption            0 = No  the Interval                               OF-USE OF-USE Billing    Value   1 = Yes Data?      Bin    Bin    Error?    ______________________________________    Current 0       Yes        B      B      NO    N-1     0       Yes        B      B      NO    N-2     0       Yes        B      B      NO    N-3     1       No         B      B      NO    N-4     X       No         A      B      YES    N-5     X       No         A      B      YES    • "       "          "      "      "    • "       "          "      "      "    • "       "          "      "      "     N-46   X       No         A      "      "     N-47   X       No         A      B      YES    ______________________________________

Additional functionality is achieved using a more complex approach tothe time-of-use billing problem in the presence of a power outage. Itwill be shown that this approach, known as "Time-of-use Metering withAsynchronous Counters," preserves time-of-use billing unambiguously inscenarios where only one outage occurs on the string of N consumptionvalues. If multiple outages occur, the consumption values in the stringprior to the first outage and after the last outage can be unambiguouslytime stamped. Intermediate values cannot be time stamped and need aspecial algorithm to classify their billing periods.

"Time-of-use Metering with Asynchronous Counters" is born from the factthat the encoder device 14 has no battery backup and no clock that isactively synchronized to a clock in the interrogate/receiver device 18."Time-of-use Metering with Asynchronous Counters" accomplishes timesynchronization with the reading technology in the interrogate/receiverdevice 18 in a passive manner. A counter is used in both the encoderdevice 14 and in the interrogate/receiver device 18. The encoder device14 counter and the interrogate/receiver device 18 counter are notsynchronized. They are asynchronous.

For "Time-of-use Metering with Asynchronous Counters" each individualencoder device 14a-14c transmits the count value of its counter alongwith its history of consumption messages. The following paragraphsdiscuss how combining this counter with the power outage flags allowsfor the prediction of the outage duration, where and when the firstpower outage started, and where and when the last power outage ended.The diagram in FIG. 10 depicts the encoder device 14 counter and theinterrogate/receiver device 18 counter in use under normal powerconditions. The slopes of the encoder device 14 counter and theinterrogate/receiver device 18 counter selected are arbitrary and couldas well be reversed or the slopes of the encoder device 14 counter andthe interrogate/receiver device 18 counter could be the same.

The algorithm for "Time-of-use Metering with Asynchronous Counters"works as follows. At the time denoted in FIG. 10 as 1, 2, 3, and 4, theinterrogate/receiver device 18 decoded a valid message from the encoderdevice 14. With the value of the interrogate/receiver device 18 counterat these samples, the interrogate/receiver device 18 uses the encoderdevice 14 counter to determine the time slope of the encoder device 14counter.

At each received sample point, the slope of the encoder device 14counter, its last received count, and the correspondinginterrogate/receiver device 18 counter are stored by theinterrogate/receiver device 18. Knowing this information, for eachsubsequent received sample from the encoder device 14, the counter valueof the encoder device 14 counter can be predicted by theinterrogate/receiver device 18. To enhance robustness, a rolling averageapproach may be used.

Assume the situation in which a power outage condition has occurredsomewhere between samples 2 and 3. FIG. 11 depicts the counterperformance in such situation. The interrogate/receiver device 18receives the Encoder device 14 message at time 3. It uses the storedslope, the encoder device 14 counter, and the interrogate/receiverdevice 18 counter values from the last read (at time 2) to predict theexpected encoder device 14 counter at time 3, CNT_(P3). This value isthen compared to the actual value of the encoder device 14 counter attime 3, CNT_(A3). A difference in the counters indicates that an outageoccurred. This is double checked by investigating the power outageflags, indicating the occurrence of at least one power outage.

The total power outage time can be found from the difference betweenthese two counters. The mathematics show:

ΔRC=Interrogate/receiver device 18 Counter Count Difference BetweenCNT_(P3) and CNT_(A3)

M_(E) =Encoder Device 14 counter Async Count-Line Slope Referred toInterrogate/receiver device 18 Counter

T_(ORC) =Power Outage Duration, Referred to the Interrogate/receiverdevice 18 Counter

T_(O) =Power Outage Duration, Referred to Real Time

    CNT.sub.A2 +ΔRC×M.sub.E =CNT.sub.P3            (1)

    CNT.sub.A2 +(ΔRC-T.sub.ORC)×M.sub.E =CNT.sub.A3 (2)

Algebraically operating on (1) and (2) leads to: ##EQU1##

If the interrogate/receiver device 18 counter is designed to veryclosely approximate real time, T_(ORC) ≅T_(O). If not, another similarcalculation needs to be made to convert T_(ORC) to real time.

An example serves best to describe the time stamping algorithm. First,take the case where only one outage occurred in the string of Nconsumption values. This is shown in FIG. 12. The example will show thatfor the case of only one outage within the N samples, all interval s canbe unambiguously time stamped.

For simplicity, only the first 17 of the N consumption interval s areshown in FIG. 12. In the example, a single power outage occurs. Ithappens within the interval marked 9. For this interval, the poweroutage flag will be set.

A time outage can be attached to all interval s 1-8 if the intervalduration, t.sub.Δ, is known a priori {1.25 min, 2.5 min, 5.0 min}. Thisis readily done by back tracking from the time at which the message wasreceived.

Previous discussions showed how the total outage time, T_(O), can bedetermined. Subtracting the sum of this value and the duration of oneinterval from the time where interval 8 started gives the time at thebeginning of interval 9 or equivalently, the time at the end of interval10. From thereon, the remaining interval s can be time tagged. ##EQU2##

The only ambiguity is the actual time within interval 9 where the powerwas lost. Since the overall interval length, t.sub.Δ, is either chosenfrom {1.25 min, 2.5 min, 5.0 min}, the ambiguity is relatively small.However, it is suggested that this ambiguity fully meets specifiedperformance.

In order to meet the specified performance, assume the system operatesover a given period without any power outages. With the same choice ofconsumption interval s, the time-of-use rate transition can happenanywhere within the interval . The system will use a market acceptabletechnique to determine where the consumption data within that intervalwill be billed. The same algorithm applies in the single power outagecase.

If a time-of-use rate transition occurs within the interval of poweroutage, from a consumption point of view no more potential consumptioncould occur in this interval than in an interval of no power outage.This must be the case since power is applied over the same duration eventhough the time duration may be much longer. Therefore, the same errorexists in billing independent of power outage.

A potentially more serious case arises incident to multiple outages thatoccur in a given interval . This may introduce some ambiguity. FIG. 13shows the counter performance in case of multiple outages.

Just as in the one outage case, the total power outage time period canbe determined by comparing the predicted counter value at time 3 to theactual counter value. It can be shown that the difference between thepredicted and actual encoder device 14 counters can be used to predictthe total power outage duration. The prediction is independent of thenumber of outages.

Referring to the example of FIG. 13, interval s 3 and 9 have their poweroutage flags set, indicating that a power outage has occurred at bothinterval s 3 and 9. The interval s in time after (1, 2) and before (10,11 . . .) can be easily time stamped. Interval s 1 and 2 can be timestamped by back tracking from the message receipt time. The mathematicsneeded to determine the start of interval 9 are shown by the followingequation: ##EQU3##

The "2" in the above formulation is the number of interval s containinga power outage and the "5" is the number of full interval s betweenpower outages.

Now that the start of interval 9 is known, all preceding interval s canbe time tagged. As stated earlier, there is too much ambiguity toaccurately time stamp the interval s between the power outages. Apresumably market-acceptable approach for dealing with the ambiguity isto add up all of the consumption in this ambiguous region and spread itevenly throughout the ambiguous region. Time outages are known for thebeginning and end of the outage so is then easily determined over thatperiod and applied to the proper time-of-use rate. For insurance, theinterrogate/receiver device 18 then sends along an estimation flag tothe billing system 30 to alert the billing system 30 at the electricutility that the actual data was not known.

What is claimed is:
 1. A metering sensor and communication system forcommunicating data related to metered consumption of electrical energyto provide support for time-of-use and demand billing in the presence ofat least one power outage event, the metering communication systemcomprising:a. a meter sensor for sensing power consumption and forsensing power outage events, the sensor generating an output signalrelated to at least the sensed power consumption and power outageevents: b. an encoder device having;means for communication with themeter sensor for receiving the output signal therefrom beingcommunicatively coupled to the meter sensor; means for periodicallygenerating an encoded RF signal for transmission by the encoder device,the signal having a plurality of discrete components, each of saidcomponents being related to electrical power consumption over a selectedinterval of time, said components including consumption parameter dataand meter identification data, the signal further having a power outageflag associated with each discrete component, the flag being set for aninterval of time during which a power outage is sensed; and encodercounter means for incrementally increasing a count as a function oftime, the encoder counter means being powered by the electrical powerbeing metered; and c. an interrogate/receiver device having;decodermeans being communicatively coupled to the encoder device for decodingthe encoded RF signal received from the encoder device; and receivercounter means for incrementally increasing a count as a function oftime, the receiver counter means being asynchronous with respect to theencoder counter means.
 2. The metering system of claim 1 wherein thereceiver counter means counts at a rate substantially equal to a realtime counter.
 3. The metering system of claim 1 wherein theinterrogate/receiver device flags the decoded RF signal received fromthe encoder device prior to transmission to a billing system for eachinterval in which the consumption of electrical energy is estimated. 4.The metering system of claim 1 wherein the interrogate/receiver devicedetermines the difference between a predicted and an actual encodercounter means count to predict a total power outage duration.
 5. Themetering system of claim 4 wherein the interrogate/receiver devicedetermines the difference between a predicted and an actual encodercounter means count to predict a total power outage duration of aplurality of power outages.
 6. The metering system of claim 1 whereinthe encoder device includes a microprocessor for receiving discreteelements of code, the microprocessor having a buffer assigned in anon-volatile memory, a pointer in the microprocessor indicating aposition in the buffer corresponding to a N-1 value, the N-1 value beinga differentially encoded consumption value which occurred at a mostrecent consumption interval.